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SubjectRe: [RFC][PATCH 0/7] perf trace: general-purpose scripting support, v2
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On Wed, 2009-11-25 at 09:28 +0100, Peter Zijlstra wrote:
> On Wed, 2009-11-25 at 01:15 -0600, Tom Zanussi wrote:
> > sched::sched_wakeup 0 01238.657997033 6183 firefox comm=firefox, pid=6199, prio=120, success=1, target_cpu=1
> > sched::sched_switch 1 01238.657991740 7140 firefox prev_comm=firefox, prev_pid=7140, prev_prio=120, prev_state=S, next_comm=firefox, next_pid=6199, next_prio=120
> >
> > min_wakeup_latency: -5293
>
> Looks like we missed a clock update on the cross cpu wakeup, Mike was
> busy plugging those holes -- I've been starting at a patch that might
> cure this (amongst other things).

Hmm, current -tip should have that cured as per:

---
commit 055a00865dcfc8e61f3cbefbb879c9577bd36ae5
Author: Mike Galbraith <efault@gmx.de>
Date: Thu Nov 12 11:07:44 2009 +0100
sched: Fix/add missing update_rq_clock() calls

kthread_bind(), migrate_task() and sched_fork were missing
updates, and try_to_wake_up() was updating after having already
used the stale clock.

Aside from preventing potential latency hits, there' a side
benefit in that early boot printk time stamps become monotonic.

Signed-off-by: Mike Galbraith <efault@gmx.de>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1258020464.6491.2.camel@marge.simson.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
LKML-Reference: <new-submission>

diff --git a/kernel/sched.c b/kernel/sched.c
index 3c11ae0..701eca4 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2017,6 +2017,7 @@ void kthread_bind(struct task_struct *p, unsigned int cpu)
}

spin_lock_irqsave(&rq->lock, flags);
+ update_rq_clock(rq);
set_task_cpu(p, cpu);
p->cpus_allowed = cpumask_of_cpu(cpu);
p->rt.nr_cpus_allowed = 1;
@@ -2115,6 +2116,7 @@ migrate_task(struct task_struct *p, int dest_cpu, struct migration_req *req)
* it is sufficient to simply update the task's cpu field.
*/
if (!p->se.on_rq && !task_running(rq, p)) {
+ update_rq_clock(rq);
set_task_cpu(p, dest_cpu);
return 0;
}
@@ -2376,14 +2378,15 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state,
task_rq_unlock(rq, &flags);

cpu = p->sched_class->select_task_rq(p, SD_BALANCE_WAKE, wake_flags);
- if (cpu != orig_cpu)
+ if (cpu != orig_cpu) {
+ local_irq_save(flags);
+ rq = cpu_rq(cpu);
+ update_rq_clock(rq);
set_task_cpu(p, cpu);
-
+ local_irq_restore(flags);
+ }
rq = task_rq_lock(p, &flags);

- if (rq != orig_rq)
- update_rq_clock(rq);
-
WARN_ON(p->state != TASK_WAKING);
cpu = task_cpu(p);

@@ -2545,6 +2548,7 @@ static void __sched_fork(struct task_struct *p)
void sched_fork(struct task_struct *p, int clone_flags)
{
int cpu = get_cpu();
+ unsigned long flags;

__sched_fork(p);

@@ -2581,7 +2585,10 @@ void sched_fork(struct task_struct *p, int clone_flags)
#ifdef CONFIG_SMP
cpu = p->sched_class->select_task_rq(p, SD_BALANCE_FORK, 0);
#endif
+ local_irq_save(flags);
+ update_rq_clock(cpu_rq(cpu));
set_task_cpu(p, cpu);
+ local_irq_restore(flags);

#if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
if (likely(sched_info_on()))



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